127 Knock after rebuild

jusjofok · #1 06-01-2011, 11:23 PM

Hello guys, new to the forum here. I have a 127 with 42" mower, tiller, front blade and back blade. Have owned it for a few months now.

When I first got this mower I noticed the engine made a rattling noise and it progressively got worse. This not being my first rodeo with Kohler engines I figured it was the balance gears if they were still installed. I tear the engine (K301) down and find the balance gears both about to let go, the snap rings were about 3/4 worn through and they wobbled like a 40 year old push mower wheel. While I was there I noticed the piston had quite a bit of play and the rod had some galling in it. I had the crank turned .010 and the cylinder bored to .030 over (it had a .020 piston in it) by a reputable machine shop. I purchased a new piston and rod from Stens as I have had good luck with their parts in the past and threw it back together. Cranked it up and it was quiet as a mouse. I started to mow my yard with it and about 15 minutes into it I started noticing a knock again. It doesn't do it under heavy load but when you back off the throttle from revving it, it rattles down to an idle (just like I have always heard a bad rod sound). This is the first one I have put back together without checking all clearances on the machined parts first. Changing timing doesn't help this thing and I can hear the knock with a screwdriver all over the engine.
Will the PTO basket make a noise that sounds identical to a rod knock or is that just my wishful thinking? Cam play was about .023 when I took it apart and I shimmed it down to .005. Valve clearances are good and there is very little play in the guides, no bubbles through WD-40 with a blow gun on the port side.
Another thing, it had quite a bit of blowby even after 45 minutes of pulling and was extremely hot, I couldn't touch the points cover for over a second. Any ideas what is going on?
Justin

william1041200 · #2 06-02-2011, 12:47 AM

You are at an advantageous point in your troubleshooting. Pull the pto off and check it by loading it running up a hill. If that makes no difference, triple check the timing. Overheating is all due to good electrical parts and timing in my experience. Well, as long as engine and fins and shroud are clean.. Seeming as little is left, check your valve clearances. Maybe the lifters got switched intake to exhaust.

jusjofok · #3 06-03-2011, 08:36 AM

Found the problem. Never trust your machinist to do it right, always Plasti-gage...
Justin

mmzullo · #4 06-03-2011, 09:08 AM

Nice find. It's amazing how some of these machinest do there work. I hope he does good on the parts.

Merk · #5 06-03-2011, 06:59 PM

Quote:

by jusjofok
This is the first one I have put back together without checking all clearances on the machined parts first.

And

I purchased a new piston and rod from Stens as I have had good luck with their parts in the past and threw it back together.

I wouldn't blame the machinist. It sounds like you did a poor checking and odering parts. Not sure where the parts came from.....It's the assembler responsibility to make sure the parts are right. The first quote proves you didn't check parts very well.

Kohler rods have a hole in the beam between the wrist pin and crank journal. I'm not sure about Stens rods. I don't use them.

Plasti-gage is a poor thing to gage a part. The only gages I use to check cylinder bore and crank pin/journal are micrometers and bore gages.

Quote:

by mmzullo
I hope he does good on the parts.

The shop/party who supplied the parts is not responsibile for this mess. It is the assembler fault.

For the record....I've been a machinist for 36 years. I measure my parts before and after my local automotive machine shop works on my motors. I will give you a copy of all dimensions I check if I build you a motor. My shop will give me a copy of all dimensions they check if I ask them to.

jusjofok · #6 06-03-2011, 09:11 PM

Merk,
I kind of take offense to that. I don't blame the machinist, I blame the tools. If his tools aren't calibrated there is no way he can hit his numbers. I worked as a machinist full time for 9 years while I was getting my engineering degree. Don't be fooled, I am not the typical engineer. Most of those years I was a manual machinist for tool and die and all parts associated with breathable air compressors, we also did a lot of automotive, ATV, watercraft, farm and oil field machine work. Learned to program about 3 years before moving away (and leaving most all my measurement tools behind). Being that I always did my own machine work using checked to standards tools, I trusted this machinist would do the same. By the way I checked the crank and it is .0034 below minimum tolerance on the un-touched journal surface, and about 2 tenths out of round. I don't believe this is a Stens part problem so don't think they are inferior parts, I have never had any issue with them before in normal use or even severe use. In this case I cannot say for sure the rod bore was in spec, that only fortifies the "measure before you assemble" moral. Also, not all internet users are dumb, so please be cautious where you put your emphasis.

The hole in the beam to signify .010" under standard size is universal. This particular rod will end up modified for an insert and shelved for later use.

Plasti-gage is a great tool, it's a fabulous sanity check, you might want to try it sometime to see how accurate it can be when used correctly.

mmzullo, I will not be asking the machinist to make good on this deal. To make it good he would have to buy me a crank (since .010 under is all that is available) or have it plasma-sprayed and risk further damage, I don't see any reason he should do that when I can make it work as is. My old man always told me "boy, if you don't ever mess up...you are dead." Next time I use him I will bring along my measurement tools or just make the trip back home and use the machine shop where the only person there is to blame is myself.

Dobre den.
Justin

AMCJavelin74 · #7 06-03-2011, 10:21 PM

Most of us are (I think it's right) dobre naravi around here, nothing personal in terms of being blunt and sometimes upsetting others. (dobre naravi= good humored, assuming I am right).

As for plastigauge, it's good stuff. Just use it the right way. I don't think it's as good as a calibrated mic, but being that it's implied that the parts were just assembled upon receiving them, I think there's the problem.

1. Clean the parts. Shavings and such can lurk on new parts.
2. Measure the clearances. If the clearances are good, it ought to at least run for a little bit without knocking.
3. Stens seems to generally make good parts. I'd trust anything they make here in the USA. I'd avoid China parts.

Overheating can be caused by the timing not set properly... I think if the timing is retarded too much. I do know it'll have spark knock if it's advanced too much.

Merk · #8 06-03-2011, 10:52 PM

Quote:

by jusjofok
I don't blame the machinist, I blame the tools. If his tools aren't calibrated there is no way he can hit his numbers.

and

Quote:

by jusjofok
Also, not all internet users are dumb, so please be cautious where you put your emphasis.

I never said all internet users were dumb...An engineering degree doesn't make someone smart. Your comment about never trusting a machinist to do it right was out of line. WE wouldn't be having this discussion if you didn't make that statement. The problem is the person who put the motor together didn't do the job right......not the machinist.

Quote:

by jusjofok
Plasti-gage is a great tool, it's a fabulous sanity check, you might want to try it sometime to see how accurate it can be when used correctly.

I've used the plasti-gage in the past. It is easier, faster and more accurate to use a micrometer and bore gage to check the parts in questions than plasti-gage.